The 20-year-old from Brooklyn, Iowa was last seen while on a run on July 18. She was staying alone with the dogs at the home of her high school sweetheart while he and his brother were out of town.

At a press conference on Monday, Mitch Mortvedt of the Iowa Division of Criminal Investigation urged the public to think back on others' behavior in the days surrounding her disappearance.

"Often there are individuals who are unknowingly associated with the offender of a crime and may be in a position to observe behavioral changes in that person," he said. "They will recognize the change, and may even question them about it, but will not relate the change to that person's involvement in a crime."

Here's what we know about the night college student Mollie Tibbetts disappeared.

Mortvedt said investigators are still exploring every potential scenario to try to figure out what happened to Mollie.

"It is possible that Mollie came into contact with someone who has caused her harm," he said. "This person may not necessarily be a member of our community but likely has some familiarity with the area."

Authorities are asking for the public's help acquiring more information about several areas in and around Brooklyn on the night Tibbetts went missing and have created a form for sharing this information on the 'Finding Mollie' website. The website also shows a map of the areas of interest.

Mortvedt highlighted specific behaviors that could be worth sharing a tip with investigators.

Change in normal routine, which might include missing school, work, or routine engagements without a plausible explanation

A vehicle unexpectedly taken to a repair shop or sold/disposed of

Unexpected or intensive cleaning of a vehicle, possibly at an unusual time of day

Unexplained lack of contact or inability to get in touch with someone you know the evening of July 18th into the morning of July 19th

Altering of physical appearance (growth or removal of facial hair, change in cut or color of hair)

Displays of anxiety, nervousness, stress or irritability

Unexplained injuries

Changes in consumption of alcohol, drugs or cigarettes

Changes in sleep patterns

Interest in the status of the investigation, including close attention to media coverage or an unwillingness to discuss the investigation